In a typical railway train braking system, each vehicle is fitted with a brake pipe extending along its length that is coupled to the vehicle's brake cylinders through service and emergency reservoirs and various valves. At each end of the vehicle, the brake pipe is coupled to a "glad hand" connector through an angle cock and a flexible hose. During assembly of a train, the glad hand connectors are interconnected to form a continuous brake pipe extending from the locomotive of the train to the last vehicle thereof. The locomotive includes a source of air pressure that is coupled to the locomotive's brake pipe by various valves, including one or more master control valves accessible to the locomotive engineer.
When the brake pipe interconnections have been made, the angle cock at the far end of the last vehicle is closed and the remaining angle cocks are opened to accordingly form a continuous, closed brake pipe extending from the locomotive to the last vehicle. Through the valves of the locomotive, the brake pipe is charged from the source of air pressure to a predetermined pressure value (e.g., 85 psi). This predetermined brake pipe air pressure causes the pistons in the brake cylinders at each vehicle to be withdrawn to effect a full brake release, and pressurizes the various reservoirs.
When a brake application is desired, one of the master control valves in the locomotive is actuated by the engineer so as to result in a reduction in brake pipe air pressure at the locomotive which thereafter rapidly propagates along the brake pipe. At each vehicle, the valves sense the differential between reservoir air pressure and brake pipe air pressure. When this differential exceeds a predetermined value (e.g., 2 psi), the valves cause the reservoir air pressure to be coupled to the brake cylinders in proportion to the magnitude of the pressure differential to accordingly extend the piston and thus apply the brakes in proportion to the magnitude of the pressure differential. In order to release the brakes after a brake application, the engineer actuates one of the master control valves to cause the brake pipe air pressure to be restored to the full release value (e.g., 85 psi) if a full brake release is desired or to an intermediate value if a partial brake release is desired.
Railway train braking systems may encounter a number of problems in operation.
First, one of the angle cocks between the locomotive and the last vehicle may not have been opened, resulting in inoperable brakes in the portion of the train rearward of the closed angle cock.
Second, there may be a leak in the brake pipe or its associated interconnections at any vehicle rearward of the locomotive. In such a case, the maximum brake pipe air pressure that can be obtained at the vehicles rearward of the leak may not be sufficient to apply or release the associated brakes.
Third, it must be remembered that it is the differential between brake pipe air pressure and reservoir air pressure that causes application and release of the brakes. Taking as an example a desired full release of the brakes following a brake application, it takes a considerable amount of time for the reservoirs distance from the locomotive to be recharged to the full release brake pipe air pressure. During this time, a desired reapplication of the brakes represented by a brake pipe air pressure reduction of the locomotive may result in the predetermined pressure differential being obtained at vehicles proximate the locomotive but not at vehicles distant from the locomotive. Accordingly, a greater brake pipe air pressure reduction than that normally used must be made to obtain brake application at the distant vehicles. Upon repeated, successive brake applications, the brake pipe air pressure reduction at the locomotive must be progressively increased to obtain brake application at the distant vehicles. At some point, the reservoir air pressures at the distant vehicles will not be sufficient to provide a brake application no matter what the amount of brake pipe air pressure reduction at the locomotive.
From the foregoing discussion, it can be appreciated that it would be extremely useful for the locomotive engineer to be continuously apprised of the lowest air pressure in the brake pipe, i.e., that at the far end of the last vehicle in the train. Heretofore, no means has been developed by which such continuous "last vehicle" brake pipe air pressure monitoring may be made. The prior art does teach many types of apparatus for monitoring brake pipe air pressure; however, most of these prior art apparatus are designed for brake pipe air pressure monitoring at the locomotive. The only exception known to the inventor is a railway brake pressure monitor in which a pressure switch is provided at the last vehicle and coupled with the far end of the brake pipe. When the monitored brake pipe air pressure drops below a predetermined value (e.g., 45 psi) below which the brakes cannot be applied, the pressure switch provides a switching action that is transmitted via radio to a remote location. Although this railway brake pressure monitor provides useful safety information concerning a possible closed angle cock or a leak, it is not capable of providing information useful in assuring the proper and efficiency application and release of the brakes throughout the train.